This invention relates to the operation and control of internal combustion engines. Specifically it relates to operation and controls for extending over temperature running of an engine.
In order to provide adequate heat rejection for the full operating range of an internal combustion engine of an automotive vehicle, such engines are equipped with cooling systems in which a liquid coolant is circulated through coolant passages in the engine to absorb heat and then through a radiator to reject heat. For any of a number of different reasons, it is possible that coolant may be lost from the cooling system and if a sufficient amount of coolant loss occurs, then the engine will begin to overheat. Such overheating gives rise to a greater amount of friction within the engine so that a greater throttle opening is required to maintain a given engine speed. This will result in an even greater quantity of heat being generated within the engine and a more rapid rise in the temperature of the engine and associated components. Therefore, if speed is maintained the engine will eventually reach a temperature at which it will cease to operate due to seizure of the engine mechanism such as piston seizure, crankshaft seizure or camshaft seizure. By the time the engine ceases running, many components will have reached extremely high temperatures and may be irreversibly damaged. However, in some cases it will be possible to restart the engine after cooling off, and it will be possible to run the engine at a reduced level of performance, although this can be hazardous since an unknown amount of damage has likely been done leading to uncontrolled engine operating conditions.
In general, the vehicle will be capable of traveling a certain amount of distance, say X miles, from the point of initial coolant loss until the engine ceases to operate. The use of new materials for certain engine components, such as a plastic intake manifold, for example, may result in the inability of such parts to withstand the increased temperatures that would occur in an all metal engine that is run until the engine ceases. Accordingly, a vehicle that has an engine equipped with such a non-metallic component will likely be incapable of operating the X miles distance referred to above, from the time of initial coolant loss. This reduction in operating range would be unwelcome and attributable directly to the plastic component.
The present invention relates to a novel engine control philosophy that addresses the loss of engine coolant in an engine containing a major plastic component, such as an intake manifold, so that an unwelcome reduction in the operating range of the vehicle after initial coolant loss is avoided. Another aspect of the invention relates to an electronic control circuit for implementing this novel control philosophy.
The invention arises through the recognition of the fact that a reduction in the engine load will result in the engine producing less heat, and therefore being capable of operating longer, when overheating is detected. The manner in which the load is reduced is a unique aspect of the invention and involves the attenuation of an engine load signal to the engine electronic control unit (ECU) when overheating is sensed.
An engine ECU controls engine operation in accordance with different inputs to the ECU. One of these inputs is a signal representative of engine load. A common way to measure engine load is by means of a manifold absolute pressure (MAP) sensor. The MAP sensor provides an output voltage corresponding approximately linearly to the engine load with higher voltage typically representing higher engine load. When an over temperature condition is detected, the MAP sensor output voltage is deliberately limited thereby resulting in the ECU receiving an engine load signal that at least at times is lower than the actual MAP sensor (engine load) signal. Accordingly, the load that is seen by the ECU appears less than it actually is and the ECU will, therefore, act to produce less engine power. As a result, heat is generated at a lower rate enabling the engine to run for a longer period of time before the temperature rises to a critical level. In this way, the operating range of an engine that has a major plastic component, such as the intake manifold, is not reduced from the operating range that it would have if all metal construction were used. The invention, therefore, provides a reduction or elimination of the destructive effects of coolant loss and the dangerous operation of a damaged engine may be avoided. The use of a MAP sensor is preferred over other load sensors, such as airflow sensors, since the MAP sensor will result in a leaning of the air fuel ratio which will cause a reduction in cylinder temperatures and an excess of cooling air to be introduced into the engine. It will also provide obvious driving symptoms to the driver of the vehicle that something is wrong with the engine before a sudden unsignaled cessation of engine operation occurs.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.